This is a new project, aimed at identifying genes involved in maintaining endothelial cell (EC) quiescence. Such genes may conceivably serve as suppressor genes of angiogenesis. We are using a molecular biology technique, known as differential display, to demonstrate genes differentially expressed by EC. Aortic EC under the following conditions were used: 1) actively growing at low density; 2) quiescent, contact inhibited monolayers; 3) intact aortas (not cultured). The goal of this study is to isolate genes preferentially expressed by the contact inhibited EC from quiescent monolayers and/or the intact aortas. Pure cultures of aortic EC populations were isolated from fresh cynomolgus monkey aortas, by passing them through two rounds of flow sorting, using a fluorescent CD31 antibody. Quiescence of confluent EC monolayers was tested by measuring bromodeoxyuridine uptake. cDNA libraries were generated from actively growing and quiescent aortic EC, and are currently being amplified by the polymerase chain reaction (PCR) technology for further analysis.